The present invention is concerned with adjusting the frequency of an oscillator, and is particularly concerned in its preferred embodiment with adjusting the free running frequency of a voltage controlled oscillator in a television receiver so that it is near enough to a target frequency to permit a phase locked loop to lock in the frequency.
The principal object of the present invention is to provide a circuit which automatically adjusts the free running frequency of a voltage controlled oscillator (VCO) so that it is close enough to the target frequency for the phase locked loop to lock the frequency.
A further object of the present invention is to provide an efficient automatic tuning circuit for a VCO thereby to permit a narrowing of the bandwidth otherwise required in the phase locked loop which correspondingly becomes more immune to noise.
Still another object of the present invention is to provide a circuit which eliminates the requirement for factory tuning as well as the effects of aging and temperature drifts in the VCO circuit.